You are in: eMedicine Specialties > Emergency Medicine > IMPLANTABLE DEVICES Pacemaker and Automatic Internal Cardiac DefibrillatorArticle Last Updated: May 25, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Maria Vasilyadis, MD, Staff Physician, Department of Emergency Medicine, New York University Medical Center Maria Vasilyadis is a member of the following medical societies: American Academy of Emergency Medicine, American Medical Association, and American Medical Student Association/Foundation Coauthor(s): Robert Allen Hessler, PhD, MD, FACEP, Associate Professor of Emergency Services, New York University School of Medicine; Assistant Director, Department of Emergency Services, Bellevue Hospital Center and New York University Medical Center; Lawrence C Brilliant, MD, Clinical Assistant Professor, Department of Primary Care and Community Services, Hahnemann University; Hahnemann University; Attending Physician, Department of Emergency Medicine, Doylestown Hospital; Barry M Weinberger, DO, Assistant Professor, Department of Cardiology, Temple University Hospital Editors: James Li, MD, Assistant Professor, Division of Emergency Medicine, Harvard Medical School; Board of Directors, Remote Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; A Antoine Kazzi, MD, Chief of Service, Department of Emergency Medicine, Medical Director of the Emergency Unit, American University of Beirut; John Halamka, MD, Chief Information Officer, CareGroup Healthcare System, Assistant Professor of Medicine, Department of Emergency Medicine, Beth Israel Deaconess Medical Center; Assistant Professor of Medicine, Harvard Medical School; Charles V Pollack, Jr, MD, MA, FACEP, Professor, Department of Emergency Medicine, University of Pennsylvania College of Medicine; Chairman, Department of Emergency Medicine, Pennsylvania Hospital Author and Editor Disclosure Synonyms and related keywords: pacemakers, automatic internal cardiac defibrillator, ICD, cardiac contraction, cardiac tachydysrhythmia, implantable cardioverter-defibrillators, ICDs BASIC CONCEPTSSection 2 of 10
  Introduction Emergency medicine physicians encounter the diversity and medical complexity of a given population on a daily basis. These entities are mirrored in the patients that they see. Among these patients are those with pacemakers and implantable cardioverter-defibrillators (ICDs). Given the numerous issues that may arise with these devices, emergency physicians must understand their common problems in order to manage them effectively. Many of these conditions often may require an electrophysiologist for complete evaluation. This article introduces the usual issues that are encountered with these devices and rescue techniques that may aid in rectifying some of the complications that are commonly seen. Pacemaker basics Permanent pacemakers are devices that provide electrical stimuli to cause cardiac contraction during periods when intrinsic cardiac electrical activity is inappropriately slow or absent. They function by sensing intrinsic cardiac electric potentials. If these potentials are too infrequent or absent, electric impulses are mechanically transmitted to the heart, thereby stimulating myocardial contraction. An ICD is a specialized device designed to directly treat a cardiac tachydysrhythmia. If a patient has a ventricular ICD and the device senses a ventricular rate that exceeds the programmed cut-off rate of the ICD, the device performs cardioversion/defibrillation. Alternatively, the device, if so programmed, may attempt to pace rapidly for a number of pulses to attempt pace-termination of the ventricular tachycardia. Note that newer devices are a combination of ICD and pacemaker in one unit. These combination ICD/pacemakers are implanted in patients who require both devices. Patients presenting to the emergency department may complain of early symptoms of presyncope, palpitations, or weakness. More pronounced presentations may include heart block or a tachydysrhythmia. Most complications occur close to the time the device was placed and may include wound dehiscence, infection, or thrombophlebitis. These may or may not be evident on physical examination. Fever, coarse breath sounds, or heart murmurs may further aid in making the diagnosis. Simply put, pacing systems consist of a pulse generator and pacing leads. With permanent systems, endocardial leads are inserted into the venous system, usually via the subclavian, axillary, or cephalic vein, and advanced to the right ventricle and/or atrium. Newer and still experimental pacing systems may have 2 atrial leads, one in the right atrial appendage and the other either in the coronary sinus or at the os of the coronary sinus, with the ventricular lead in the right ventricle, either at the apex or at the outflow tract. This dual site or biatrial pacing system is used to prevent or minimize bouts of atrial fibrillation. Another still experimental system is biventricular pacing with 2 ventricular leads, one in the right ventricle and the other in a venous branch of the coronary sinus pacing the left ventricle. The pulse generator is placed subcutaneously or submuscularly and connected to the leads. Alternatively, epicardial leads can be implanted surgically onto the heart's surface. These usually are used in children because implanted endocardial leads eventually become too short as children grow. Permanent leads are unipolar or bipolar. To complete the electrical circuit in a unipolar system, the metallic pulse generator serves as part of the circuit and is connected to the positive electrode whereupon the negative electrode touches the endocardium. In a bipolar system, both electrodes are within the heart. Unipolar systems are smaller, less prone to damage but are incompatible with ICD systems unlike bipolar configurations. Temporary systems use an external pulse generator with leads placed via transvenous, transcutaneous, or transthoracic approaches. Transcutaneous leads are the easiest to use for rapid initiation of temporary pacing and the most commonly used mode of pacing in the emergency department. However, transvenous leads provide the most reliable pacing mechanism and are a good transition to more permanent systems. For transvenous temporary pacing, semirigid catheters are inserted through a central venous access and usually require fluoroscopy for proper placement. ECG monitoring (specifically V1) is essential to track catheter positioning. For example, P-wave morphology is initially inverted and becomes upright as the catheter is in line with the SA node. QRS morphology is also initially inverted, becoming more isoelectric and then upright as the tip is placed in the apex. An injury pattern resembling ST elevation ensures that the catheter tip is in proper positioning for pacing. Semifloating or flexible balloon-tipped catheters can be used in emergencies since they can be positioned using blood flow alone. Transcutaneous pacing is discussed in detail in a separate article (see External Pacemakers). Transthoracic catheters are inserted into the right ventricle through a left parasternal or subxiphoid approach and can be used in a cardiac arrest situation. This procedure has many complications and rarely produces effective mechanical cardiac contraction and is almost never performed. Pulse generators contain, among other things, a battery, an output circuit, a sensing circuit, and a timing circuit. The battery most commonly used in permanent pacers is a lithium-iodide type and has a life span of 5-8 years. Temporary transvenous pacers use a household 9-volt battery. Pacemaker energy output is dependent upon the signal amplitude and pulse width. Signal amplitude is measured in electrical units of volts or milliamperes. Pulse width is a measure of output duration and is measured in milliseconds. For proper permanent pacer operation, signal amplitude and width are set high enough to reliably achieve capture of the myocardium, yet low enough to prolong battery life. Pulse generators can be set to a fixed-rate (asynchronous) or demand (synchronous) mode. In the fixed-rate mode, an impulse is produced at a set rate and has no relationship to the patient's intrinsic cardiac activity. This mode carries a small but inherent danger of producing lethal dysrhythmias should the impulse coincide with the vulnerable period of the T wave. In the demand mode, the sensing circuit searches for an intrinsic depolarization potential. If this is absent, a pacing response is generated. This mode can closely mimic the intrinsic electric activity pattern of the heart. PACING CODESSection 3 of 10
The Heart Rhythm Society and the British Pacing and Electrophysiology Group (BPEG) have developed a code to describe various pacing modes. This is illustrated in Table 1. Pacemaker Code Used to Describe Various Pacing Modes
A = Atrium V = Ventricle D = Dual (both chambers) O = None T = Triggered I = Inhibited D = Double (Atrial triggered and ventricular inhibited) P = Simple programmability M = Multiprogrammable C = Communicating (telemetry) R = Rate adaptive The first 3 letters are used most commonly. More modern pacemakers have multiple functions. A pacemaker in VVI mode denotes that it paces and senses the ventricle and is inhibited by a sensed ventricular event. Alternatively, AAT mode represents pacing and sensing in the atrium, and each sensed event triggers the generator to fire within the P wave. The DDD mode denotes that both chambers are capable of being sensed and paced. This requires two functioning leads, one in the atrium and the other in the ventricle. In the ECG, each QRS is preceded by two spikes. One indicating the atrial depolarization and the other indicating the initiation of the QRS complex. Given that one of the leads is in the right ventricle, a left bundle-branch pattern may also be evident upon the ECG. Note that a two-wired system need not necessarily be in DDD mode, since the atrial or ventricular leads can be programmed off. Additionally, single tripolar lead systems are available that can sense atrial impulses and either sense or pace the ventricle. Thus, this system provides for atrial tracking without the capability for atrial pacing and can be used in patients with atrioventricular block and normal sinus node function. Pacemaker programming can be performed noninvasively by an electrophysiologist or cardiologist. Because of the myriad of pacemaker types, patients should carry a card with them providing information about their particular model. This information is crucial when communicating with the cardiologist about a pacer problem. Most pacemaker generators, however, have an x-ray code that can be seen on a standard chest x-ray. The markings, along with the shape of the generator, may assist with deciphering the manufacturer of the generator and pacemaker battery. This may be helpful in the event a patient neither recalls the company nor has the permanent pacemaker card. MAGNET INHIBITIONSection 4 of 10
Placing a magnet over a permanent pacemaker causes sensing to be inhibited by closing an internal reed switch. This only temporarily "reprograms" the pacer into the asynchronous mode, where pacing is initiated at a set rate. It does not turn the pacemaker off. Each pacemaker type has a unique asynchronous rate for beginning-of-life (BOL), elective replacement indicator (ERI), and end-of-life (EOL). Therefore, application of a magnet can determine if the pacer's battery needs to be replaced. Further interrogation, or manipulating of the device, should be performed by an individual skilled in the technique. Patients should carry a card that contains information about their particular pacemaker, since these rates are dependent on the manufacturer and the model. PACEMAKER INDICATIONSSection 5 of 10
Absolute indications for pacemaker placement include the following:
Relative indications include the following:
Temporary emergency pacing is indicated for therapy of significant and hemodynamically unstable bradydysrhythmias and prevention of bradycardia-dependent malignant dysrhythmias. Examples of therapeutic indications for temporary pacing include refractory symptomatic sinus node dysfunction, complete heart block, alternating bundle-branch block, new bifascicular block, and bradycardia-dependent ventricular tachycardia. Examples of indications for prophylactic temporary pacing include insertion of a pulmonary artery catheter in a patient with an underlying left bundle-branch block, use of medications that may cause or exacerbate hemodynamically significant bradycardia, prophylaxis during the perioperative period surrounding cardiac valvular surgery, Lyme disease or other infections (Chagas disease) that cause interval changes, and prolonged PR intervals. ICD placement is generally for cases where the previous cardiac arrest was due to an irreversible cause or in patients with an undetermined origin and continued ventricular tachycardia or fibrillation despite medical interventions. PACEMAKER COMPLICATIONSSection 6 of 10
Major pacemaker complications include infection, thrombophlebitis, and a condition known as pacemaker syndrome. This is a phenomenon where a patient might actually feel worse after pacemaker placement and present with progressive worsening of their symptoms of congestive heart failure. This is mainly due to the loss of atrioventricular synchrony whereby the pathway is reversed and now has a ventricular origin. Major pacemaker malfunctions include failure to output, failure to capture, and failure to sense correctly. Failure to output Failure to output occurs when no pacing spike is present despite an indication to pace. This may be due to battery failure, lead fracture, a break in lead insulation, oversensing (inhibiting pacer output), poor lead connection at the takeoff from the pacer, and "cross-talk" (ie, a phenomenon seen when atrial output is sensed by a ventricular lead in a dual-chamber pacer). Pseudomalfunction is a type of output failure characterized by a phenomenon termed hysteresis. This is essentially the dulling of an effect when forces acting upon the body are changed or altered. This occurs when a pacer is set to sense below the lower pacing rate limit. For example, if the lowest pacing rate programmed is 60 beats per minute (bpm), a pacer set to sense down to an intrinsic rate of 50 bpm, a hysteresis rate, begins to pace at 60 bpm when the patient's intrinsic rate falls below 50 bpm. It continues to pace at the lower rate limit of the pacemaker, in this example 60 bpm, until it again senses intrinsic activity and acts as a back-up mechanism. This sensed event inhibits pacing, and the pacemaker again permits the intrinsic rate to go down to 50 bpm before pacing at 60 bpm. Modern pacemakers may operate at the upper limit and have the capability to also control tachydysrhythmias. Management of pacer output complications includes medications to increase the intrinsic heart rate and placement of a temporary pacer. A chest radiograph is warranted to check pacer leads, with close scrutiny to evaluate for possible lead fracture, which occurs most commonly at the clavicle/first rib location. The patient's pacer identification card should be obtained and his/her electrophysiologist/cardiologist consulted. Failure to capture Failure to capture occurs when a pacing spike is not followed by either an atrial or a ventricular complex. This may be due to lead fracture, lead dislodgement, a break in lead insulation, an elevated pacing threshold, myocardial infarction at the lead tip, certain drugs (eg, flecainide), metabolic abnormalities (eg, hyperkalemia, acidosis, alkalosis), cardiac perforation, poor lead connection at the takeoff from the generator, and improper amplitude or pulse width settings. Management of pacer capture complications is the same as for output complications, with extra consideration given to treating metabolic abnormalities and potential myocardial infarction. Oversensing Oversensing occurs when a pacer incorrectly senses noncardiac electrical activity and is inhibited from correctly pacing. This may be due to muscular activity, particularly oversensing of the diaphragm or pectoralis muscles, electromagnetic interference such as MRIs, or lead insulation breakage. More recently, cellular phones held within 10 cm of the pulse generator may elicit this response. Undersensing Undersensing occurs when a pacer incorrectly misses intrinsic depolarization and paces despite intrinsic activity. This may be due to poor lead positioning, lead dislodgment, magnet application, low battery states, or myocardial infarction. Management is similar to that for other types of failures. Operative failures A final category of pacer failures is termed operative. This includes malfunction due to mechanical factors, such as pneumothorax, pericarditis, infection, skin erosion, hematoma, lead dislodgment, and venous thrombosis. Treatment depends on the etiology. Pneumothoraces, being dependent on size, may require chest thoracostomy. Erosion of the pacer through the skin, while rare, requires pacer replacement and systemic antibiotics. Hematomas may require drainage. Lead dislodgment usually occurs within 2 days following implantation of a permanent pacer and may be seen on chest radiography. If the lead is floating freely in the ventricle, malignant arrhythmias may develop. Thrombosis is rare and usually presents as unilateral arm edema. Treatment includes arm elevation and anticoagulation. Advanced life support protocols, including defibrillation, may safely be executed in patients with pacemakers in place. Sternal paddles are placed at a safe distance (10 cm) from the pulse generator. Temporary transcutaneous pacing may become necessary in cases of myocardial infarction. ICD COMPLICATIONSSection 7 of 10
Major ICD complications are similar to those found in pacemakers. Major ICD malfunctions include operative failures, sensing and/or pacing failures, inappropriate cardioversion, ineffective cardioversion/defibrillation, and device deactivation. Operative failures are identical to those found in regular pacemakers. Sensing problems similar to those seen with pacers may occur with ICDs. An example of appropriate failure to treat is when a device has a cut-off rate of 180 bpm. If ventricular tachycardia occurs at 160 bpm, the device, appropriately, fails to cardiovert the patient since the rate of the dysrhythmia is below the programmed rate cut-off. Inappropriate cardioversion is the most frequent complication associated with ICDs and one that patients are very aware of, provoking pain and anxiety in these otherwise unsuspecting individuals. This should be considered if a patient presents in atrial fibrillation or if a patient has received multiple shocks in rapid succession without premonitory symptoms. For example, if, as in the example given above, the patient develops atrial fibrillation with a ventricular response of greater than or equal to 180 bpm, the device delivers therapy. Newer devices have certain enhancements that allow discrimination between such rhythms. Causes, other than a supraventricular dysrhythmia, include T-wave oversensing, lead fracture, lead insulation breakage, electrocautery, MRI, and electromagnetic interference. Use of a magnet over the ICD inhibits further shocks. It does not, however, inhibit bradycardiac pacing should the patient require it. In some older devices, application of a magnet produces a soft beep for each QRS complex. If the magnet is left on for approximately 30 seconds, the ICD is disabled and a continuous tone is generated. To reactivate the device, the magnet must be lifted off the area of the generator and then replaced. After 30 seconds the beep returns for every QRS complex. Failure to deliver cardioversion is caused by failure to sense, lead fracture, electromagnetic interference, and inadvertent ICD deactivation. Management includes external defibrillation or cardioversion and antidysrhythmic medications. If external defibrillation is required, attempt to keep the generator out of the shock wave. Defibrillation that affects the generator may cause total failure of the device. However, do not withhold therapy because of fear of damaging the ICD. Note that the rescuer may feel a mild shock wave if the patient's internal defibrillator activates during chest compressions. However, no reports of this causing any grave injuries in rescuers have been documented. Ineffective cardioversion may be due to inadequate energy output, rise in the defibrillation threshold (which may be due to antiarrhythmic medications, eg, amiodarone, flecainide, phenytoin), myocardial infarction at the lead site, lead fracture, insulation breakage, and dislodgment of the leads or of the myocardial cardioversion patches. The latter still are seen sometimes in patients who had ICDs implanted during open chest surgery prior to approximately 1993. Many ICDs deliver a programmed set of therapies per dysrhythmic episode. The number of therapies per episode is manufacturer specific. If a delivered therapy does not terminate an arrhythmia, the device goes to the next programmed therapy. For example, a total of 6 attempts at defibrillation are attempted per episode of ventricular fibrillation. The device attempts defibrillation and then reevaluates the cardiac rhythm. If the arrhythmia persists, it delivers therapy number two and so on, until all 6 attempts have been delivered. Once this occurs, the device does not deliver therapy until a new episode is declared. Note that initial therapy for ventricular tachycardia may be overdrive pacing rather than simple cardioversion, as mentioned earlier in this article. ICDs do not prevent all sudden deaths, and acknowledging that cardiac arrest is not necessarily a malfunction of the ICD is important. The device may have delivered the required shocks properly but was ineffective in correctly treating the triggering rhythm. SUMMARYSection 8 of 10
The goal of this article is to orient the reader to the basic function and use of pacemakers/ICDs and the important complications in both of these devices. This knowledge allows the practitioner to understand and troubleshoot the various causes of pacemaker or ICD failure and initiate appropriate therapy. The patient's electrophysiologist/cardiologist can also be an invaluable resource in these cases and should be contacted early during the emergency department evaluation. MULTIMEDIASection 9 of 10
REFERENCESSection 10 of 10
Pacemaker and Automatic Internal Cardiac Defibrillator excerpt Article Last Updated: May 25, 2006 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
